IEC 61508 requires human factor issues to be considered in the determination of hazards and hazardous events (7.4.2.3 of IEC 61508-1) and in the design of the E/E/PE safety-related system (7.4.5.3 of IEC 61508-2). For E/E/PE safety-related protection systems, there are three principal areas that need to be considered:

• human actions or errors that can place a demand on the E/E/PE safety-related protection system – these need to be identified and quantified;
• human failure to respond effectively to alarms or take other actions that would otherwise reduce the demand on the E/E/PE safety-related protection system;
• human failure in testing and maintenance of the E/E/PE safety-related protection system, reducing its effectiveness and increasing the probability of failure on demand.

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